1. Field of the Invention
The present invention relates to a light-receiving circuit, in particular, relates to an light-receiving circuit for an avalanche photodiode.
2. Related Prior Art
It has been well know that various bias controlling circuits to apply a bias voltage to an avalanche photodiode (APD), for example, a Japanese Patent applications published as H11-284445 and 2004-071892 have been disclosed typical examples of the bias controlling circuit. In such circuits, a resistor is connected in serial to the APD, i.e., between the bias source and the APD, to restrict an excess bias voltage to the APD. A photo current generated by the APD, which corresponds to an optical input power, flows in this resistor to cause a voltage drop thereat, and makes the bias voltage applied to the APD to decrease by this voltage drop. Accordingly, the bias voltage to the APD decreases as the input optical power increases, thereby reducing the multiplication factor M of the APD at the large optical input power and preventing the APD from breaking down.
However, the method to have the bias voltage to depend on the optical input power by using the resistor connected in serial to the APD has an disadvantage that the power dissipation of the resistor increases as the optical input power increases. Therefore, one of the objects of the present invention is to provide a light-receiving circuit for the avalanche photodiode to reduce the power dissipation.